Radio receiving circuit arrangement



Oct. 27, 1953 F, Q'wlLLlAMs 2,657,306

RADIO RECEIVING- CIRCUIT ARRANGEMENT Filed Aug. 21, 194e 2 sheets-sheet 1 J n". *E llll S/ @M'Hl 2 lm il LD o- 2 Sheets-Sheet 2 /IVVE/VTO FREnERlc, (1M/ummm @y MIA; wv Mu F. C. WILLIAM S RADIO RECEIVING CIRCUIT ARRANGEMENT AFI oct. 2'7, 195s Filed Aug. 21 1946 Patented Oct. 27, 1953 wit@ Relire CIRCUIfl-l AI UfwrGElwEli1-v i Frederic Cllaliflwillims, Great-Malia@ ilgi.- lane, assigner,- aq Ministflof'srlr in His Maestre. Gsve Applic a'nugust 21, 194.6, serial. 692,084.

Grealritain March 11.91415;

Sentieri 1, Public Law 6 99, August 8, 1946 Caire- (C1-"garen creation! of the superfegenerafire.:ieiil de bed in the specification 'or my (zo-pending U- S,- atent applicationirel Nel- 692,085,5-1@ August 21,1946, now' E atent'N'. 2,592,7'7`7`gra 'ted April l5; 1952 has.v been 'fund te, he impartire; by the'aprilicatin'of thernie'sent ijl- "SiiDer#igenerattive; receivers VV"are riotrieu'sly critical'inthe adjustment of their circuit parameterstctgive reliable and sensitiye reception. The se' ivity normally v" ies from' time td'tinie with change of' irequency,`aer1al aging,

angesandwith componeriit:yaZ

ce er to another.

circuit arrangement descrip d thesptech ication'r'eferred to, lc,oifnlsrises `a' u ti/'e' Vreceiyer Which is'opferating u y ons conditions and operation of. th@ the',` desired degree or vsltalc'lity isid partieular circuit arrange of a super-regenerativ Valve'. addition'to the quench Voltage, a l* agewhich renders the 'alve inoperative 3y siredQand the tuned circuit, which yariab a Wide renee, is fC-.Ommfm'fofa tra .,mitti which has pulse fee'd-loacly cohnecti traiv 'g1-ifi; Diinculties or, mainte ,1 this cir uit'are` thusinre eddue n plexity f. the circuits cup ,l

ve, tree ieem? vente @f 'ene primarily due to radio frequency oscillations in the receiver oneachA quench cyclebuilding up frmthe random noise 'in the receiver tuned cir? cuits and, therefore,` has a very strong GQmDDIlGllt at quench frequency although the receiver utpirt also'contains components spread out in frequency over'the Whole of the pass hand Of, the receuyver. According to the `present invention, a circuit arrangement including a Valve 'arranged to operateregeneratively thegain'is stabilised in the absence of' anv input signal, bymeans of a direct current Voltage.: Which is btained'by rectification of current representing noi'se in the: circuit, the direct current 'Voltage 'being fed"t0 th ej Valli@ in such a manner that any tendency towards alteration' of the generaljlevel nois'eoscillationeY in the output `circuit of the valve is resisted; Ldr elimi-v Inl a particular circuit arrangement embodying the invention, thevalve'iscperated super-'regeneratively and the directfcurrent voltage is derived fromaucircuit tuned to the; quenching.4 frequency employed; the Yrectiied'voltage loeingfed'as abiasing potential to the control grid of said'jvalve. The tuned circuit employed may be: constituted by' a coupling 'transformer thev output fromwhich i's rectified'hefore 'application 'tof thels'upereregenerative valve. 'i i i "In 'orderthat the invention may be more clear- 1y mderstood'iand readily carried into? effect', a1- ternatve circuit arrangements designedto operate in'acco'rdance therewith will `now be more fully' described bytvay'ofexample, Withr'eierence to'tle accompanying drawings in' whichi ligureV l shows'a respondercircuit suitable for indicating identification of; V for example, an" aircraftfimder'interrogationas describedn'the'specication of myn cti-pending *Ui SPatentf applicatinS.'No. 692,085, filed August21, 1946, and Eigi'eZshows amodigcation. H f Referring to` *Figure lof the drawings, an incoming interrogating signal in the form of a nurnberof. separate radio frequency 'pulsesiis'fe'dfrom an aerial socket, P8, through a couplingcoilyLrl tothe'rn'ain oscillatoryfcircuitjl; C`9the tuning of which "is repeatedly swept once every three secondsthroughA a frequency fband' off 30" megaycl'e'spersecond betweenl'! and 187 nregacycles pei-Second; :Uhr l c' ri l,. ,vnl 'The'reoeived signal is fed to a super-regenerative'valvef'VzZ, to' which* quenching oscillations `areal'spV fed from amquenching' valve'V-rdlhe Vsignal'riutput from Valve'litriggers Van oscillator vali/.evt'Whichis normally biased tocutv off.: JIjhis triggeringaction isi'effected by `feeding vthefreceived signal oscillations occurring in the circuit LB, C9 to a diode V4 where they are rectified and the rectied signal then applied to the grid of an amplifier V5, which is coupled in turn to a valve V6 having a cathode load resistance RIB. The output voltages, in the form of positive-going voltage pulses appearing at the cathode end of the resistance Ri are fed back to the control-grid or" the oscillator valve V3 Where they act to reduce the negative bias potential and so permit the valve to burst into oscillation. As the resonant circuit L6, C9 will still be tuned to the frequency or the received signal which initiated the triggering action, the iinal result is the generation and radiation through coupling coil Ll' and the aerial socket PS o a counter part or response signal pulse for each of the received signals appearing at the output valve V6. The high-frequency oscillations persist for a period of time which is determined principally by the constants of the coupling circuit between the valve V and V6, and more particularly by the values of the condensers C25, C59, the latter of which is controlled by a signal coding switch i A.

Owing to the presence of random noise in the super-regenerative circuit, the degree of build-up applied during each quenching cycle will, in general, be variable. In order to stabilize this effect, a part of the output from the rectifier Vil is fed through a condenser CSG, to the control grid oi a valve V9, which includes in its anode circuit an iron-cored transformer Lid, L! i tuned to the quenching frequency. The voltage across the winding Lid is rectified by a diode VS, and is applied from the load resistance R22 to the grid of a valve V'i, where it appears in amplied form across the cathode resistance Riii. From here it is fed through a resistance Ril and choke L3 to the grid of the super-regenerative valve V2, and, by reducing the gain of that valve, automatically checks any increase in the general level of the noise oscillations in the tuned circuit L6, C9.

Provision is also made to inhibit the responder circuits during the operation of any other radio transmitter that may be carried by the interrogated crat. For this purpose a suppressing voltage, synchronized with the other transmitter, is applied through a socket Pl to a diode Vi i, and through a resistance to the grid of a valve Vie. The resulting negative impulses are applied by the valve Vi@ through a condenser C38 and resistance R25 to the grid of the valve V2, and through a condenser C33 and resistance R29 to the grid ci the quenching valve Vi, and throw both these valves out of action. Simultaneously a positive voltage is fed from the cathode resistance RBi of the valve VIE through a condenser C3@ to the cathode of the rectifier Vd to render that valve non-conductive. As a result the responder is temporarily rendered insensitive to all signals, including those from the local transmitter.

The aerial tuning condenser C53 is driven from a motor-generator through a cam-shaft which simultaneously controls the coding devices. One cam-operated contact, not shown periodically interrupts the high-tension supply to the valves V2, V3. Another cam, energises a relay, not

shown, to close, the switch SA which brings the condenser C59 into parallel with the condenser C2@ for variable width coding. An eXtra wide pulse may be radiated as a distress signal and for this purpose a third cam energises another relay, not shown which (a) CIQSES a, SWfCh t0 4 bring a condenser C2I into parallel with the condenser C2Il, and (b) closes a switch li to bring resistance RI3- into parallel with a resistance Ri. A switch 3 connects a condenser Cid across the cathode resistance R5 of the oscillator V3 in order to condition that circuit to the wide pulse, whilst a switch 2 serves to override the previously mentioned cam-operated H. T. control switch for the valves V2, V3 so as to provide an uninterrupted H. T. supply to the latter. A selector switch allows the operator to control the coding as required.

The arrangements for efecting cyclic Variation o the aerial tuning circuit, and for effecting signal coding form no part of the present invention and are not, therefore, described detail, the present invention being concerned, as previously indicated, with the methods of effecting stabilisation of the super-regenerative circuit by utilising the noise output of the receiver.

Referring novi.T to Figure 2 of the drawings, a super-regenerative receiver valve, V has in its anode circuit a tuned circuit, C?, coupled to the aerial, not shown, by a coil, LA.. Bias potential is applied to the cathode of the valve from a tapping in a potentiometer comprising resistances R4 and R5. The quench voltage is supplied by an oscillator valve, Vi, operating at a frequency of 300 kilo-cycles per second. The voltage from the anode of this Valve is supplied through the attenuating network, C3, to the grid of the valve V2. The output from the tuned circuit L3, C'i, is rectified by the diode, V 3, and is then passed to signal amplifying and output stages as required, connected to a terminal T.

The output from the rectiiier V3, is also fed through condenser, C9, to the grid of an amplifying valve, V4, which constitutes the rst ampli- Iier in the automatic gain stabilising circuit. The anode circuit of the valve, V6, contains a tuned output circuit, L5, C15, LS, Cl' tuned tc the quench frequency. The resulting voltage across secondary winding L6 which represents a narrow band of the noise spectrum centered about the quench frequency is rectified by a diode V5, and after smoothing by a resistance/capacity combination RIZ, CM, is applied to the grid of the direct current amplifying valve, rlhe voltage developed across the cathode load .resistance Rit is applied as a bias potential to the grid of the regenerative receiver value V2, through a resistance, R5, and has the eiiect of stabilising the operation of this valve. If, for any reason, the gain of the receiver and thus the noise voltage, tends to increase, compensation is ciected by the resultant increase in the direct current bias voltage across the resistance, R53, which, as stated, is fed to the control grid of the valve, V2, and tends to reduce the gain of that valve. This means that any tendency for the receiver noise level to change is strongly resisted and in fact, a state of equilibrium is reached.

Provided that the super-regenerative properties of either of the receiver circuits described are maintained, any variations in tuning, supply voltages, components or other disturbing factors can only cause a slight change in the receiver noise. The magnitude of this change is only a very small fraction of that which would occur in the absence of the automatic gain stabilising circuit, and depends upon the gain of that circuit. If this gain were iniinite the change in noise amplitude and, therefore, in the receiver sensitivity due to any external iniuence would be theoretically ZEI'O.

The eiect of modulation upon any signal which is being received is slight, due to the fact that the modulation frequency is generally outside the Pass band of the output circuit of the valve, V4. It' the receiver is required to operate on a pulsed transmission, as is the case with the apparatus described in my co-pending U. S. patent application S. No. 692,085 filed August 21, 1946, the pulses will have little eiect on the stabilising system until their repetition frequency exceeds 2 kcs. when the stabilising circuit described tends to bias olf the receiver reducing its sensitivity. The sensitivity to which the circuit adjusts the receiver, and thus the working gain of the receiver, may be set to .the desired value by controlling the magnitude if the direct current bias potential applied to the receiving valve, V2, in any known manner, for example, by adjustment of the resistance, RIS. The system may, therefore, be adjusted to maintain the receiver at its most sensitive state, in spite of external disturbing variations.

Although one application of the invention has been described with reference to Figure 1 of the drawings in connection with apparatus for effecting identification by means of interrogating and responding equipment, it will be seen from the example described with reference to Figure 2, to be of quite general application to regenerative circuit arrangements.

I claim:

1. A super-regenerative radio receiver circuit comprising a space discharge tube including a cathode, at least one control grid and an anode, positive feed-back means including a tuned circuit coupled between said anode and a contro-l grid for providing regeneration, signal input and output circuits coupled to said tuned circuit, a source of quenching oscillations, means for applying said quenching oscillations between the cone trol grid and cathode of said tube, a selective amplifier circuitl tuned to the frequency of said .quenching oscillations, connecting means between said signal output circuit and the input circuit of said amplifier, a rectifying device connected to the output circuit of said amplifier for converting the amplified quench frequency signal output of said amplifier into a direct-current voltage and further connection means for applying said direct-current voltage between a control grid andthe cathode of said space discharge tube to control the sensitivity thereof.

2. A super-regenerative radio receiver circuit comprising a space discharge tube including a cathode, at least one control grid and an anode, positive feed-back means including a tuned circuit coupled between said anode and a control grid for providing regeneration, signal input and output circuits coupled to said tuned circuit, a source of quenching oscillations, means for applying said quenching oscillations between the 6 control grid and cathode of said tube, a selective amplifier circuit tuned to the frequency of said quenching oscillations, connecting means between said signal output circuit and the input circuit of said amplifier, a rectifying device connected to the output circuit of said amplifier for converting the amplified quench frequency signal output of said amplier With a direct-current voltage and a direct-current thermionic amplifier circuit including a space discharge tube having an output load resistance in its cathode circuit, connection means for feeding said direct-current voltage to the input circuit of said direct-current amplifier and further connecting means between said output load resistance and the cathode and a control grid of said rst space discharge tube suitable for controlling the sensitivity of the tube by change of their relative potentials.

3. A super-regenerative radio receiver circuit comprising a space discharge tube including a cathode, a control grid and an anode, positive feed-back means including a tuned circuit coupled between said anode and a control grid for providing regeneration, signal input and output circuits coupled to said tuned circuit, a source of quenching oscillations, means for applying said quenching oscillations between the control grid and cathode of said tube, a selective amplifier circuit tuned to the frequency of said quenching oscillations, connecting means between said signal output circuit and the input circuit of said amplifier, a rectifying device connected to the output circuit of said amplifier for converting the amplied quench frequency signal output of said ainplier with a direct-current voltage and a direct-current thermionic amplifier circuit including a space discharge tube having an output load resistance in its cathode circuit, connection means for feeding said direct-current voltage to the input circuit of said direct-current amplifier and means connecting said output load resistance and the cathode and control-grid of said first space discharge tube for increasing the negative potential of said control-grid in response to an increase in amplitude of the quench frequency output of said selective amplier circuit.

FREDERIC CALLAND WILLIAMS.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,006,803 Grimes July 2, 1935 2,045,700 Dalpayrat June 30, 1936 2,147,595 Hilferty Feb. 14, 1939 2,414,992 Wheeler Jan. 28, 1947 2,429,513 Hansen Oct. 21, 1947 FOREIGN PATENTS Number Country Date 243,407 Great Britain Nov. 23, 1925 307,177 Great Britain Mar. 7, 1929 

